Posted By:
JoshI agree that Mantle's rarest card known to exist is the 1966 Punch-out. I do not believe duplicates of any of those cards exist.
Aside from cards issued (or never actually issued) as test issues that were never really produced on any sort of large scale, for cards issued on a larger scale, Mantle's rarest cards are his early Venezuelan's. 1959 & 1960 especially are extremely rare cards.